System and method for compressor motor protection

ABSTRACT

A refrigerant compressor includes an electric motor. A current sensor measures current flow to the electric motor. A switching device is configured to close and open to allow and prevent current flow to the electric motor, respectively. A maximum continuous current (MCC) device includes a stored digital value corresponding to a maximum continuous current for the electric motor. A motor protection module: communicates with the MCC device, the current sensor, and the switching device; determines a first MCC for the electric motor as a function of the stored digital value received from the MCC device; selectively sets a predetermined MCC to the first MCC; and controls the switching device based on a comparison of the current flow to the electric motor and the predetermined MCC.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 13/737,566, filed on Jan. 9, 2013, which claims the benefit of U.S. Provisional Application No. 61/585,382, filed on Jan. 11, 2012. The entire disclosures of the above applications are incorporated herein by reference in their entirety.

FIELD

The present application relates to electric motor control systems and methods and more particularly to maximum continuous current (MCC) systems and methods.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

A power source such as an electrical utility may supply alternating current (AC) power to a refrigerant compressor. The refrigerant compressor includes an electric motor that drives the refrigerant compressor. A system including the refrigerant compressor may also include one or more devices that prevent current flow to the electric motor from exceeding a predetermined value.

For example, a line break protector may be implemented such that current flows through the line break protector before flowing to the electric motor. The line break protector may include an electric heater that generates heat as current flows through the line break protector. The line break protector trips and disables current flow to the electric motor when the current flowing through the line break protector is greater than the predetermined value.

For another example, a positive temperature coefficient (PTC) device and/or a negative temperature coefficient (NTC) device may be implemented in thermal contact with a motor winding to achieve a temperature relative to the temperature of the motor. Resistances of the PTC and/or NTC devices may then be used to determine motor temperature, both directly and indirectly. One or more remedial actions, such as shutting off the motor, can be taken if the motor temperature measured or determined using the PTC and/or NTC devices is greater than a predetermined temperature.

SUMMARY

In a feature, a system is described. A refrigerant compressor includes an electric motor. A current sensor measures current flow to the electric motor. A switching device is configured to close and open to allow and prevent current flow to the electric motor, respectively. A maximum continuous current (MCC) device includes a stored digital value corresponding to a maximum continuous current for the electric motor. A motor protection module: communicates with the MCC device, the current sensor, and the switching device; determines a first MCC for the electric motor as a function of the stored digital value received from the MCC device; selectively sets a predetermined MCC to the first MCC; and controls the switching device based on a comparison of the current flow to the electric motor and the predetermined MCC.

In further features, the motor protection module opens the switching device when the current flow to the electric motor is greater than the predetermined MCC.

In further features, the motor protection module receives the stored digital value wirelessly from the MCC device using near field communication.

In further features, the motor protection module receives the stored digital value wirelessly from the MCC device using radio frequency identification (RFID).

In further features, the motor protection module receives the stored digital value wirelessly from the MCC device using a Bluetooth communication protocol.

In further features, the motor protection module determines the first MCC for the electric motor using a lookup table that relates digital values to respective first MCCs.

In further features, the MCC device is integrated with the motor protection module.

In further features, the system further includes a second MCC device. The motor protection module: determines a second MCC for the electric motor as a function of an output of the second MCC device; and selectively sets the predetermined MCC to the second MCC.

In further features, the motor protection module sets the predetermined MCC equal to a lesser one of the first and second MCCs.

In further features, the second MCC device is integrated with the refrigerant compressor and remote from the motor protection module.

In a feature, a method is described. The method includes: measuring, using a current sensor, current flow to an electric motor of a refrigerant compressor; selectively opening and closing a switching device to allow and prevent current flow to the electric motor, respectively; communicating with the current sensor, the switching device, and a maximum continuous current (MCC) device, the MCC device including a stored digital value corresponding to a maximum continuous current for the electric motor; receiving the stored digital value from the MCC device; determining a first MCC for the electric motor as a function of the stored digital value received from the MCC device; selectively setting a predetermined MCC to the first MCC; and controlling the switching device based on a comparison of the current flow to the electric motor and the predetermined MCC.

In further features, the method further includes opening the switching device when the current flow to the electric motor is greater than the predetermined MCC.

In further features, receiving the stored digital value from the MCC device includes receiving the stored digital value wirelessly from the MCC device using near field communication.

In further features, receiving the stored digital value from the MCC device includes receiving the stored digital value wirelessly from the MCC device using radio frequency identification (RFID).

In further features, receiving the stored digital value from the MCC device includes receiving the stored digital value wirelessly from the MCC device using a Bluetooth communication protocol.

In further features, determining the first MCC includes determining the first MCC for the electric motor using a lookup table that relates digital values to respective first MCCs.

In further features, the method further includes: determining a second MCC for the electric motor as a function of an output of 1 second MCC device; and selectively setting the predetermined MCC to the second MCC.

In further features, the method further includes setting the predetermined MCC equal to a lesser one of the first and second MCCs.

In further features, the second MCC device is integrated with the refrigerant compressor.

Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a heat pump system;

FIG. 2 is a functional block diagram of an example motor control system;

FIGS. 3A-3C are functional block diagrams of example current control systems; and

FIG. 4 is a flowchart depicting an example method of controlling current flow to an electric motor.

DETAILED DESCRIPTION

The following description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure.

As used herein, the term module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); an electronic circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip (SOC). The term module may include memory (shared, dedicated, or group) that stores code executed by the processor.

The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared, as used above, means that some or all code from multiple modules may be executed using a single (shared) processor. In addition, some or all code from multiple modules may be stored by a single (shared) memory. The term group, as used above, means that some or all code from a single module may be executed using a group of processors or a group of execution engines. For example, multiple cores and/or multiple threads of a processor may be considered to be execution engines. In various implementations, execution engines may be grouped across a processor, across multiple processors, and across processors in multiple locations, such as multiple servers in a parallel processing arrangement. In addition, some or all code from a single module may be stored using a group of memories.

The apparatuses and methods described herein may be implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on a non-transitory tangible computer readable medium. The computer programs may also include stored data. Non-limiting examples of the non-transitory tangible computer readable medium are nonvolatile memory, magnetic storage, and optical storage.

An original equipment manufacturer (OEM), such as a compressor manufacturer, determines a maximum continuous current (MCC) for a motor of a refrigerant compressor based on a variety of factors. For example only, the MCC for the motor may be set based on output capability of the motor (e.g., horsepower), one or more characteristics of the refrigerant compressor, the type of refrigerant, and an operating envelope. The operating envelope may include an evaporator temperature range and a condenser temperature range within which the refrigerant compressor will be allowed to operate.

The OEM may provide the refrigerator compressor with an MCC device. For example only, the MCC device may be integrated within a control module that controls the motor and the refrigerant compressor, integrated with the motor, or provided in another suitable manner. The MCC device generates an output, such as a resistance or a stored digital value. The output of the MCC device corresponds to the MCC determined by the OEM.

The control module may selectively disable current flow to the motor based on the output of the MCC device. For example, the control module may disable current flow to the motor when the output of the MCC device is outside of a predetermined range of values. The predetermined range of values may be set such that the output of the MCC device will be above or below the range when the MCC device has been open circuited or short circuited.

The control module may also determine a predetermined MCC for the motor based on the output of the MCC device. The motor draws current during operation of the refrigerant compressor. One or more current sensors measure current flow to the motor. The control module may selectively disable current flow to the motor when the current flowing to the motor is greater than the predetermined MCC.

One or more additional MCC devices may also be provided in various implementations. For example only, a system designer can provide an additional MCC device that indicates a value for the predetermined MCC that cannot be exceeded by the MCC device provided by the OEM. The system designer may provide an additional MCC device, for example, when one or more parameters of the operating envelope can be made narrower than the operating envelope used by the OEM in setting the MCC for the motor. The system designer may provide the additional MCC device(s) on a structure of the refrigeration or A/C system, away from a body of the compressor. The additional MCC device(s) may be connected with the control module via a physical connection or a wireless (e.g., near field communication) connection.

The control module determines an output (e.g., a resistance) of the additional MCC device and determines a second MCC for the motor based on the output of the additional MCC device. The control module may selectively set the predetermined MCC to the MCC determined based on the output of the MCC device or the second MCC determined based on the resistance of the additional MCC device. For example only, the control module may set the predetermined MCC equal to the lesser one of the MCCs. In this manner, if the second MCC is less than the MCC set by the OEM, the control module will disable current flow to the motor when the current flowing to the motor is greater than the second MCC. If the second MCC is greater than the MCC specified by the OEM, however, the MCC specified by the OEM will be used.

Referring now to FIG. 1, an example diagram of a heat pump system 10 is presented. Heat pump system 10 may include an indoor unit 12 and an outdoor unit 14. A heat pump system is used for illustration purposes only, and it should be understood that the present application is applicable to other systems including a motor-driven compressor, such as HVAC systems and refrigeration systems.

Indoor unit 12 may include an indoor coil or heat exchanger 16 and a variable speed indoor fan 18. Indoor fan 18 is driven by motor 20. Indoor coil 16 and indoor fan 18 may be enclosed in a housing 22 so indoor fan 18 may force air across indoor coil 16.

Outdoor unit 14 may include an outdoor coil or heat exchanger 24 and a variable speed outdoor fan 26. Outdoor fan 26 is driven by a motor 28. Outdoor coil 24 and outdoor fan 26 may be enclosed in a housing 30 so outdoor fan 26 may draw air across outdoor coil 24. Outdoor unit 14 may further include a compressor 32 connected to indoor coil 16 and outdoor coil 24. Compressor 32 may have a motor that is driven by a variable speed inverter drive as illustrated (see also FIG. 2) or a fixed speed motor.

Compressor 32, indoor coil 16, and outdoor coil 24 may be connected to generally form a loop where compressor 32, indoor coil 16, and outdoor coil 24 are arranged in series with one another and an expansion device 33 is located between indoor coil 16 and outdoor coil 24. Heat pump system 10 may include a reversing valve 34 disposed between compressor 32 and indoor and outdoor coils 16 and 24. Reversing valve 34 may enable the direction of flow between compressor 32, indoor coil 16, and outdoor coil 24 to be switched (reversed) between first and second directions.

In the first direction, heat pump system 10 operates in a cooling mode providing a flow in a direction indicated by the arrow labeled “cooling”. In the cooling mode, compressor 32 provides a fluid (e.g., a refrigerant) to outdoor coil 24. The fluid then travels to indoor coil 16 and then back to compressor 32. In the cooling mode, indoor coil 16 functions as an evaporator coil and outdoor coil 24 functions as a condenser coil.

In the second direction, heat pump system 10 operates in a heating mode providing a flow in a direction indicated by the arrow labeled “heating”. In the heating mode, flow is reversed relative to the first direction. Compressor 32 provides fluid to indoor coil 16. The fluid then travels to outdoor coil 24 and then back to compressor 32. In the heating mode, indoor coil 16 functions as a condenser coil and outdoor coil 24 functions as an evaporator coil.

Referring now to FIG. 2, a block diagram of an example motor control system is presented. Utility 102 may provide alternating current (AC) power to customer 114. The AC power may be three-phase AC power as illustrated or single-phase AC power. Customer 114 may include heat pump system 10, compressor 32, a power factor correction (PFC) system 104, a control module 106, a motor 108, a rectifier 110, a switching device 112, an inverter drive 116, and sensors 121, 122, 123, and 124.

Customer 114 may have a load that includes compressor 32 and heat pump system 10. Although one or more components depicted separately from heat pump system 10 in FIG. 2, such as compressor 32, one or more components may be integral to heat pump system 10. Motor 108 of heat pump system 10 may be integral to compressor 32 of heat pump system 10. Motor 108 may be driven directly by utility 102 via the switching device 112, but for example purposes only, is driven by variable speed inverter drive 116 of compressor 32.

Sensor 121 may measure current flow through one of the three-legs of the AC power. For example only, sensor 121 may include a current transducer (CT). Current consumption may be expressed as amperage. Sensor 121 may also measure voltage and power (e.g., in volt-amps) delivered by utility 102. Sensor 121 may also provide a watt meter reading of the real power consumed by customer 114. Sensor 121 may be located at multiple positions relative to customer 114 or utility 102. Sensor 121 may be located, for example only, downstream of switching device 112 and upstream of PFC system 104 and rectifier 110.

Sensor 122 may measure current flow through another one of the three-legs of the AC power. For example only, sensor 122 may include a CT. Current consumption may be expressed as amperage. Sensor 122 may also measure voltage and power (e.g., in volt-amps) drawn by inverter drive 116. Sensor 122 may also provide a watt meter reading of the real power consumed by customer 114. Sensor 122 may be located at multiple positions relative to customer 114 or utility 102. In various implementations, sensor 121 and sensor 122 may be implemented together within a dual sensor module 125.

PFC system 104 may be connected to receive current output by switching device 112. PFC system 104 may be any suitable device that improves a power factor of a load. For example only, PFC system 104 may include a passive PFC, such as a bank of capacitors used to balance an inductive load or an inductor to balance a capacitive load. For another example only, PFC system 104 may include a conventional active PFC system that actively provides a high power factor, such as a power factor approaching 1.0. Control module 106 may control switching of PFC system 104 if PFC system 104 is an active PFC system. Rectifier 110 may also be connected to receive current output by switching device 112.

Current may be provided to inverter driver 116 by PFC system 104 and/or rectifier 110. Inverter drive 116 drives motor 108. Inverter drive 116 may drive motor 108 at a variable speed to regulate operation of compressor 32 of heat pump system 10. Control module 106 may regulate switching of inverter drive 116 to vary the speed of motor 108.

Sensor 123 may be implemented with motor 108 and may measure a temperature of motor 108. For example only, sensor 123 may include a negative temperature coefficient (NTC) sensor, a positive temperature coefficient (PTC) sensor, a thermistor, or another suitable type of temperature sensor. Sensor 123 may measure, for example only, a magnetic wire temperature of motor 108. Sensor 123 may also measure one or more other parameters from motor 108, such as current, voltage, compressor operating speed, and/or commanded operating speed, etc. Each of sensors 121, 122, and 123 may be a single sensor or multiple sensors that provide measurements to control module 106. Sensor 124 may be a single sensor or multiple sensors that measure parameters of heat pump system 10. For example only, sensor 124 may measure discharge temperature and/or pressure, suction temperature and/or pressure, condenser temperature and/or pressure, evaporator temperature and/or pressure, compressor speed, refrigerant temperature and/or pressure, etc.

Switching device 112 may be any device or combination of devices that enable (allow) and disable (prevent) current flow to motor 108. Switching device 112 may be an electrical switch, a contactor, a relay, or another suitable type of switching device. Switching device 112 may be implemented, for example, between sensor 121 and utility 102 in various implementations. However, switching device 112 may be located in another suitable location upstream of motor 108.

Control module 106 may include a motor protection module 130. Motor protection module 130 may control switching device 112 based on one or more parameters, for example, to protect motor 108. Motor protection module 130 may control switching device 112 based on a temperature of motor 108 measured using sensor 123. For example only, motor protection module 130 may control switching device 112 to enable current flow to motor 108 when the temperature is less than a predetermined temperature. Conversely, motor protection module 130 may control switching device 112 to disable current flow to motor 108 when the temperature is greater than the predetermined temperature.

Motor protection module 130 may additionally or alternatively control switching device 112 based on a measured current consumption of motor 108. For example only, motor protection module 130 may control switching device 112 to enable current flow to motor 108 when the current is less than a predetermined maximum continuous current (MCC). Conversely, motor protection module 130 may control switching device 112 to disable current flow to motor 108 when the current is greater than the predetermined MCC. Motor protection module 130 may disable current flow to motor 108 within a predetermined period when the current is greater than the predetermined MCC.

A first MCC device (e.g., see FIGS. 3A-B) may include a resistance. The first MCC device may be integrated with control module 106 or integrated with compressor 32. Motor protection module 130 determines a first MCC based on the resistance of the first MCC device or a digital value output by the first MCC device. The resistance of the first MCC device or the digital value output by the first MCC device may be set, for example, by an original equipment manufacturer (e.g., a compressor manufacturer) to indicate an MCC for an operating envelope and characteristics of motor 108, compressor 32, and the type of fluid used. The operating envelope may include a range of evaporator temperatures and a range of condenser temperatures within which the motor protection module 130 can operate compressor 32.

Motor protection module 130 may also control switching device 112 to disable current flow to motor 108 when the output of the first MCC device indicates that the first MCC device has been short circuited or open circuited. For example, motor protection module 130 may disable current flow to motor 108 when the resistance of the first MCC device is approximately zero (short circuit) or infinity (open circuit). Disabling current flow to motor 108 when the first MCC device is open circuited or short circuited may protect motor 108 in the event that an attempt to bypass the first MCC device is made.

A second MCC device 132 may also be implemented in various implementations. Second MCC device 132 is remote from control module 106. Second MCC device 132 may be, for example, integrated with compressor 32 or mounted to a structure of a system, such as housing 30. Second MCC device 132 may also include a resistance. Second MCC device 132 may be implemented and the resistance of second MCC device 132 may be selected, for example, down the distribution chain from the original equipment manufacturer, such as by a system designer.

The resistance of second MCC device 132 may be selected to provide a second MCC. Motor protection module 130 determines the second MCC based on the resistance of second MCC device 132. Motor protection module 130 selectively sets the predetermined MCC for use in enabling and disabling current flow to motor 108 to the first MCC or the second MCC.

For example only, when the first MCC is greater than the second MCC, the motor protection module 130 may set the predetermined MCC equal to the second MCC. In this manner, current drawn by motor 108 can be limited to the second MCC specified using second MCC device 132. The system designer can choose contactor size, size of electrical wiring, fuses, and one or more electrical components based on the second MCC. Under circumstances that allow for the second MCC to be used as the predetermined MCC, cost savings may be enjoyed as smaller electrical wiring, contactors, etc. may be implemented.

When the second MCC is greater than the first MCC, however, the motor protection module 130 may set the predetermined MCC equal to the first MCC. Using the first MCC as the predetermined MCC when the second MCC is greater than the first MCC may prevent the first MCC device from being bypassed or disconnected.

In the event that one or more of control module 106, second MCC device 132, and compressor 32 are replaced (e.g., for service reasons), the motor protection module 130 can establish the predetermined MCC. For example, when the control module 106 is replaced, the new control module can determine the first and second MCCs and determine the predetermined MCC based on the first and second MCCs. When the second MCC device 132 is replaced, the control module 106 can determine the new value of the second MCC and determine the predetermined MCC based on the first MCC and the (new) second MCC.

FIGS. 3A-3C include functional block diagrams of example current control systems. Referring now to FIG. 3A, a block diagram of an example current control system is presented. Motor protection module 130 may include a first MCC device 202. First MCC device 202 may output a first voltage 206 that corresponds to a resistance of a resistor 204 of first MCC device 202. For example only, the resistor 204 may include a programmable potentiometer, such as a digitally programmable potentiometer (DPP), or another suitable type of programmable resistance device. A microcontroller, microprocessor, or other suitable device 210 may selectively set (program) the resistance of first MCC device 202, for example, based on inputs from a service tool (not shown), a network connection, and/or one or more other suitable inputs.

Microcontroller 210 selectively determines the resistance of first MCC device 202 based on first voltage 206. For example only, microcontroller 210 may determine the resistance of first MCC device 202 using one of a function and a mapping (e.g., look up table) that relates voltage to resistance and first voltage 206 as input. The function or mapping may be stored, for example, in memory 214. For example only, memory 214 may include electrically erasable programmable read only memory (EEPROM) and/or one or more other suitable tangible storage mediums.

Microcontroller 210 determines the first MCC based on the resistance of first MCC device 202. For example only, microcontroller 210 may determine the first MCC using one of a function and a mapping (e.g., look up table) that relates resistance to MCC and the resistance of first MCC device 202 as input.

Microcontroller 210 selectively enables and disables current flow to motor 108 via switching device 112 using an output 212 to a protection module 215. For example only, microcontroller 210 may set output 212 to one of a first state and a second state at a given time, and protection module may one of enable and disable current flow to motor 108 via switching device 112 based on the state of output 212. Microcontroller 210 may enable and disable current flow to motor 108 or enable and disable current flow to motor 108 in another suitable manner. For example only, microcontroller 210 may disable switching of inverter drive 116 to prevent current flow to motor 108.

Microcontroller 210 selectively disables current flow to motor 108 based on the resistance of first MCC device 202. For example only, microcontroller 210 disables current flow to motor 108 when the resistance of first MCC device 202 is outside of a predetermined resistance range. Microcontroller 210 may enable current flow to motor 108 when the resistance of first MCC device 202 is within the predetermined resistance range.

A lower boundary of the predetermined resistance range may be set sufficiently close to zero such that the resistance of first MCC device 202 being less than the lower boundary indicates that first MCC device 202 is short circuited. An upper boundary of the predetermined resistance range may be set sufficiently greater than a maximum resistance such that the resistance of first MCC device 202 being greater than the upper boundary indicates that first MCC device 202 is open circuited or that microcontroller 210 and first MCC device 202 are disconnected.

Microcontroller 210 may determine whether to determine the second MCC based on a second voltage 218. A first terminal of a current limiting resistor 222 may be connected to a voltage potential 226. A second terminal of current limiting resistor 222 may be connected to microcontroller 210 and to a first terminal of a jumper device 230. A second terminal of jumper device 230 may be connected to a ground source 234.

Whether a jumper 238 is connected between the first and second terminals of jumper device 230 controls second voltage 218. For example only, when jumper 238 is connected, jumper 238 creates a short circuit between the first terminal and the second terminal of jumper device 230 and causes second voltage 218 to be approximately equal to a first predetermined voltage. When jumper 238 is not connected, second voltage 218 is approximately equal to a second predetermined voltage.

The OEM may provide the motor protection module 130 with jumper 238 connected between the first and second terminals of jumper device 230. Microcontroller 210 may determine the second MCC based on the resistance of second MCC device 132 when second voltage 218 is approximately equal to the first predetermined voltage. In various implementations, the opposite may be true. Motor protection module 130 may be provided without jumper 238 being connected between the first and second terminals of jumper device 230, and microcontroller 210 may determine the second MCC based on the resistance of second MCC device 132 when second voltage 218 is approximately equal to the second predetermined voltage.

A first signal conditioner module 242 may be connected to second MCC device 132. First signal conditioner module 242 receives a signal (e.g., a voltage) output by second MCC device 132 that corresponds to the resistance of a resistor 246 within second MCC device 132. First signal conditioner module 242 may also output a reference voltage (not shown) to second MCC device 132. First signal conditioner module 242 outputs a third voltage 250 that corresponds to the resistance of resistor 246 of second MCC device 132. First signal conditioner module 242 may condition the signal in one or more ways to generate third voltage 250, such as by filtering, buffering, digitizing, and/or performing one or more other suitable signal conditioning functions.

Microcontroller 210 selectively determines the resistance of second MCC device 132 based on third voltage 250. For example only, microcontroller 210 may determine the resistance of second MCC device 132 using one of the function and the mapping (e.g., look up table) that relates voltage to resistance and third voltage 250 as input. Microcontroller 210 determines the second MCC based on the resistance of second MCC device 132. For example only, microcontroller 210 may determine the second MCC using one of the function and the mapping (e.g., look up table) that relates resistance to MCC and the resistance of second MCC device 132 as input.

Microcontroller 210 selectively sets the predetermined MCC equal to one of the first MCC and the second MCC. For example only, when the second MCC is not determined (e.g., when jumper 238 is connected), microcontroller 210 may set the predetermined MCC equal to the first MCC. When the second MCC is determined, microcontroller 210 may set the predetermined MCC equal to the lesser one of the first and second MCCs. In this manner, when the resistance of second MCC device 132 is set such that the second MCC is greater than the first MCC, the predetermined MCC will be set to the first MCC to prevent the first MCC from being exceeded. Additionally, when the resistance of second MCC device 132 is set such that the second MCC is less than the first MCC, the predetermined MCC will be set to the second MCC such that current consumption of motor 108 can be limited to less than the first MCC. Limiting current consumption of motor 108 to less than the first MCC may enable smaller electrical wiring and smaller electrical contactors to be used. Use of smaller electrical wiring and electrical contactors may provide a cost savings.

While the present application is discussed in terms of one second MCC device, one or more additional second MCC device may be used in various implementations. Microcontroller 210 may determine resistance(s) within the one or more additional second MCC devices, determine MCC(s) based on the resistance(s), and set the predetermined MCC equal to the smallest one of the MCCs.

In various implementations, microcontroller 210 may set the predetermined MCC equal to one of the first and second MCCs based on an output 254 of a comparator module 258. For example only, comparator module 258 may include a Schmitt trigger or another suitable type of comparator. Comparator module 258 may receive first voltage 206 (corresponding to the resistance of first MCC device 202) and third voltage 250 (corresponding to the resistance of second MCC device 132). Comparator module 258 compares first voltage 206 with third voltage 250 and generates output 254 based on the comparison.

For example only, comparator module 258 may set output 254 to a first state when the relationship between first and third voltages 206 and 250 is such that the first MCC is less than the second MCC. Once comparator module 258 has set output 254 to the first state, comparator module 258 may transition output 254 to a second state when the relationship between first and third voltages 206 and 250 is such that the second MCC is less than the first MCC by at least a predetermined amount. When output 254 is in the first state, microcontroller 210 may set the predetermined MCC equal to the first MCC. Microcontroller 210 may set the predetermined MCC equal to the second MCC when output 254 is in the second state.

A second signal conditioner module 262 may be connected to sensor 121. Second signal conditioner module 262 receives a signal (e.g., a voltage) output by sensor 121 that corresponds to current flowing through switching device 112. Second signal conditioner module 262 outputs a fourth voltage 266 that corresponds to the current flowing through switching device 112. Second signal conditioner module 262 may condition the signal in one or more ways to generate fourth voltage 266, such as by filtering, buffering, digitizing, and/or performing one or more other suitable signal conditioning functions. Microcontroller 210 may determine a first current using one of a function and a mapping that relates voltage to current using fourth voltage 266 as input.

A third signal conditioner module 270 may be connected to sensor 122. Third signal conditioner module 270 receives a signal (e.g., a voltage) output by sensor 122 that corresponds to current flowing to inverter drive 116. Third signal conditioner module 270 outputs a fifth voltage 274 that corresponds to the current flowing to inverter drive 116. Third signal conditioner module 270 may condition the signal in one or more ways to generate fifth voltage 274, such as by filtering, buffering, digitizing, and/or performing one or more other suitable signal conditioning functions. Microcontroller 210 may determine a second current using one of the function and the mapping that relates voltage to current using fifth voltage 274 as input.

Microcontroller 210 selectively enables and disables current flow to motor 108 based on current flow to motor 108 and the predetermined MCC. The first current, the second current, a current determined based on the first and second currents, or another suitable measured current may be used as the current flow to motor 108. Microcontroller 210 disables current flow to motor 108 when the current flow to motor 108 is greater than the predetermined MCC. Conversely, microcontroller 210 enables current flow to motor 108 when the current flow to motor 108 is less than the predetermined MCC.

When the current flow to motor 108 is greater than the predetermined MCC, microcontroller 210 may wait to disable the current flow to motor 108 for a predetermined period after the current flow to motor 108 becomes greater than the predetermined MCC. If the current flow to the motor 108 becomes less than the predetermined MCC during the predetermined period, microcontroller 210 may override the decision to disable current flow to motor 108 and maintain current flow to motor 108.

Microcontroller 210 may disable current flow to motor 108 during the predetermined period, however, when one or more predetermined conditions are satisfied. For example only, microcontroller 210 may disable current flow to motor 108 during the predetermined period when a rate of change of the current flow to motor 108 (di/dt) is greater than a predetermined rate of change. Additionally or alternatively, microcontroller 210 may disable current flow to motor 108 during the predetermined period when an acceleration of the current flow to motor 108 (d²i/dt²) is greater than a predetermined acceleration. Additionally or alternatively, microcontroller 210 may disable current flow to motor 108 during the predetermined period when the current flow to the motor 108 becomes greater than a predetermined current that is a predetermined percentage greater than the predetermined MCC. For example only, the predetermined percentage may be 5 percent, 10 percent, 15 percent, or another suitable percentage. Additionally or alternatively, microcontroller 210 may disable current flow to motor 108 during the predetermined period when an electric charge value is greater than a predetermined electric charge value. Microcontroller 210 may determine the electric charge value, for example, based on an integral (mathematical) of the current flow to motor 108 during the period. For example, the mathematical integral may be ∫(i−MCC_(pre))*dt, where MCC_(pre) is the predetermined MCC value and I is the measured current value, in order to put the reference at the predetermined MCC value. When the measured current exceeds the predetermined MCC value, the electric charge value (e.g., in Coulombs) increases due to the positive difference between the measured current value and the predetermined MCC value. A negative difference between the measured current value and the predetermined MCC value will cause the electric charge value to decrease. The integral may continue summing until it exceeds the predetermined electric charge value, wherein the switching device 112 would be opened by microcontroller 210. Additionally, the integral will continue summing until the electric charge value returns to zero due to the amount and duration of the current dropping below the predetermined MCC value.

A fourth signal conditioner module 278 may be connected to sensor 123. Fourth signal conditioner module 278 receives a signal (e.g., a voltage) output by sensor 123 that corresponds to a temperature of motor 108. Fourth signal conditioner module 278 outputs a sixth voltage 282 that corresponds to the temperature of motor 108. Fourth signal conditioner module 278 may condition the signal in one or more ways to generate sixth voltage 282, such as by filtering, buffering, digitizing, and/or performing one or more other suitable signal conditioning functions.

Microcontroller 210 may determine the temperature of motor 108 using one of a function and a mapping that relates voltage to temperature using sixth voltage 282 as input. Microcontroller 210 disables current flow to motor 108 when the temperature of motor 108 is greater than the predetermined temperature. Conversely, microcontroller 210 enables current flow to motor 108 when the temperature of motor 108 is less than the predetermined temperature.

Microcontroller 210 may also selectively enable and disable current flow to motor 108 based on one or more other parameters. For example only, microcontroller 210 may disable current flow to motor 108 when a shell temperature is greater than a predetermined temperature, when a compressor discharge temperature is greater than a predetermined temperature, and/or when one or more suitable disabling conditions occur. Microcontroller 210 may enable current flow to the motor 108 when the disabling conditions are not occurring.

While the present application is discussed in terms of devices with resistances that convey information regarding MCC, the resistances of onboard and remote devices may also be used to set predetermined values used in enabling and disabling current flow to motor 108. For example only, the resistances of onboard and remote devices may also be used to set the predetermined temperature.

When microcontroller 210 determines that current flow to motor 108 should be disabled via opening switching device 112, microcontroller may determine a response time. The response time may be or correspond to a period between a time when the decision to disable current flow to motor 108 is made and a time when microcontroller 210 commands opening of switching device 112. Microcontroller 210 may determine the response time, for example, based on a difference between the current to motor 108 and the predetermined MCC, a rate of change of the difference, and/or one or more other suitable parameters. For example only, the response time may decrease as the difference increases and/or as the rate of change of the difference increases and vice versa.

Referring now to FIG. 3B, another functional block diagram of another example current control system is presented. Microcontroller 210 may receive a reference voltage 302 from a reference voltage source (VREF) 304. A resistor 306 is connected between reference voltage source 304 and node 308. Resistor 246 of second MCC device 132 is connected between node 308 and a ground source 310, such as ground source 234. As such, the voltage at node 308 corresponds to the resistance of resistor 236 of second MCC device 132.

Microcontroller 210 may also receive the voltage at node 308. Microcontroller determines the resistance of resistor 246 of second MCC device 132 based on the relationship between reference voltage 302 and the voltage at node 308. Microcontroller 210 determines the second MCC based on the resistance of resistor 246. Microcontroller 210 sets the predetermined MCC based on the first and second MCCs and selectively disables current flow to motor 108 based on the predetermined MCC as discussed above.

Second MCC device 132 may output a value indicative of the second MCC to motor protection module 130 via a wired connection (e.g., as discussed above in conjunction with the examples of FIGS. 3A and 3B). Alternatively, second MCC device 132 may communicate the second MCC or a value indicative of the second MCC to motor protection module 130 wirelessly.

Referring now to FIG. 3C, a functional block diagram of another example current control system is presented. For example only, second MCC device 132 may communicate the second MCC or a value indicative of the second MCC to motor protection module 130 using near field communications, such as radio frequency identification (RFID), a Bluetooth communication protocol, or another suitable type of wireless communications.

Motor protection module 130 may include a communications module 320 and an antenna 324. Antenna 324 receives wireless output from second MCC device 132 and relays the output from second MCC device 132 to communications module 320. Communications module 320 may output one or more signals that prompt or cause second MCC device 132 to generate the output in various types of wireless communication. Communications module 320 provides output that is indicative of the second MCC to microcontroller 210. Microcontroller 210 can determine the second MCC based on the output. Microcontroller 210 sets the predetermined MCC based on the first and second MCCs and selectively disables current flow to motor 108 based on the predetermined MCC as discussed above.

Referring now to FIG. 4, a flowchart depicting an example method of controlling current flow to motor 108 is presented. At 404, control determines the resistance of first MCC device 202. Control may determine whether the resistance of first MCC device 202 is within the predetermined resistance range at 408. If false, control may disable current flow to motor 108 at 412, and control may end. If true, control may proceed with 416. When the resistance of first MCC device 202 is outside of the predetermined resistance range, first MCC device 202 may be short or open circuited.

At 416, control determines the first MCC based on the resistance of first MCC device 202. Control determines the first MCC as a function of the resistance of first MCC device 202. For example only, control may determine the first MCC using one of a function and a mapping that relates resistance to MCC. Control determines whether the second MCC should be determined at 420. If false, control may set the predetermined MCC equal to the first MCC at 424 and continue with 440. 440 is discussed further below. If true, control may continue with 428.

Control determines the second MCC at 432. Control determines the second MCC based on the output of second MCC device 132. Control determines the second MCC as a function of the resistance of second MCC device 132. For example only, control may determine the second MCC using one of a function and a mapping that relates resistance to MCC. Control may determine the first and second MCCs using the same or different functions and/or mappings. Control may set the predetermined MCC equal to the lesser one of the first and second MCCs at 436.

Control selectively disables current flow to motor 108 based on the predetermined MCC and current flowing to motor 108 at 440. More specifically, control disables current flow to motor 108 when the current to motor 108 is greater than the predetermined MCC. When the current to motor 108 is greater than the predetermined MCC, control may determine the response time. The response time may be or correspond to a period between the time when the current to motor 108 is greater than the predetermined MCC and a time when control commands opening of switching device 112. Control may determine the response time, for example, based on the difference between the current to motor 108 and the predetermined MCC, a rate of change of the difference, and/or one or more other suitable parameters. For example only, the response time may decrease as the difference increases and/or as the rate of change of the difference increases and vice versa. The current flow to motor 108 may be provided using one or more current sensors, such as sensor 121 and/or sensor 122. Control may disable current flow to motor 108 by opening switching device 112.

The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims. 

What is claimed is:
 1. A system comprising: a refrigerant compressor including an electric motor; a current sensor that measures current flow to the electric motor; a switching device configured to close and open to allow and prevent current flow to the electric motor, respectively; a maximum continuous current (MCC) device that includes a stored digital value corresponding to a maximum continuous current for the electric motor; a motor protection module that: communicates with the MCC device, the current sensor, and the switching device; determines a first MCC for the electric motor as a function of the stored digital value received from the MCC device; selectively sets a predetermined MCC to the first MCC; and controls the switching device based on a comparison of the current flow to the electric motor and the predetermined MCC.
 2. The system of claim 1 wherein the motor protection module opens the switching device when the current flow to the electric motor is greater than the predetermined MCC.
 3. The system of claim 1 wherein the motor protection module receives the stored digital value wirelessly from the MCC device using near field communication.
 4. The system of claim 1 wherein the motor protection module receives the stored digital value wirelessly from the MCC device using radio frequency identification (RFID).
 5. The system of claim 1 wherein the motor protection module receives the stored digital value wirelessly from the MCC device using a Bluetooth communication protocol.
 6. The system of claim 1 wherein the motor protection module determines the first MCC for the electric motor using a lookup table that relates digital values to respective first MCCs.
 7. The system of claim 1 wherein the MCC device is integrated with the motor protection module.
 8. The system of claim 1 further comprising a second MCC device, wherein the motor protection module: determines a second MCC for the electric motor as a function of an output of the second MCC device; and selectively sets the predetermined MCC to the second MCC.
 9. The system of claim 8 wherein the motor protection module sets the predetermined MCC equal to a lesser one of the first and second MCCs.
 10. The system of claim 8 wherein the second MCC device is integrated with the refrigerant compressor and remote from the motor protection module.
 11. A method comprising: measuring, using a current sensor, current flow to an electric motor of a refrigerant compressor; selectively opening and closing a switching device to allow and prevent current flow to the electric motor, respectively; communicating with the current sensor, the switching device, and a maximum continuous current (MCC) device, the MCC device including a stored digital value corresponding to a maximum continuous current for the electric motor; receiving the stored digital value from the MCC device; determining a first MCC for the electric motor as a function of the stored digital value received from the MCC device; selectively setting a predetermined MCC to the first MCC; and controlling the switching device based on a comparison of the current flow to the electric motor and the predetermined MCC.
 12. The method of claim 11 further comprising opening the switching device when the current flow to the electric motor is greater than the predetermined MCC.
 13. The method of claim 11 wherein receiving the stored digital value from the MCC device includes receiving the stored digital value wirelessly from the MCC device using near field communication.
 14. The method of claim 11 wherein receiving the stored digital value from the MCC device includes receiving the stored digital value wirelessly from the MCC device using radio frequency identification (RFID).
 15. The method of claim 11 wherein receiving the stored digital value from the MCC device includes receiving the stored digital value wirelessly from the MCC device using a Bluetooth communication protocol.
 16. The method of claim 11 wherein determining the first MCC includes determining the first MCC for the electric motor using a lookup table that relates digital values to respective first MCCs.
 17. The method of claim 11 further comprising: determining a second MCC for the electric motor as a function of an output of 1 second MCC device; and selectively setting the predetermined MCC to the second MCC.
 18. The method of claim 17 further comprising setting the predetermined MCC equal to a lesser one of the first and second MCCs.
 19. The method of claim 17 wherein the second MCC device is integrated with the refrigerant compressor. 